You guys know that you can turn off the pm?
/setpm off
Besides that, spamming/harassment is a rulebreak as I already stated in the previous post..
What I suggested is addition only to phone mechanic to avoid getting spammed with new notifications if some troll decided to send you 100 messages of whatever. So basically, you can send a message only to a number you have in your contact list.
As in your shared it personally yourself, you gave the permission to that person to leave notifications to you and not that someone else gave them the number and then they spammed you..